Fire control system



Feb. 2, 1937. H, MURTAGH AL 2,069,417

FIRE CONTROL SYSTEM Filed Jan. '10, 1934 5 Sheets-Sheet l INVE TORS final/1? L/fimulvaa\ Hus/1 HURT/96H Bib/raw ajgfr N6 THEI ATTORNEY. 1

Feb. 2, 1937. H. MURTAGH El AL FIRE CONTROL SYSTEM Filed Jan. 10, 1934 5 Sheets-Sheet 2 GOHPVTER Feb. 2, 1937. H. MURTAGH El AL 2,069,417

FIRE CONTROL SYSTEM Filed Jan. 10, 1934 3 Sheets-Sheet 3 INYENTORS 65 IiTHURL hhMnyGsFAM/MNMI/IGH 60 i\ I .N I f I 62 I H RA RNEY.

Patented Feb. 2, 1937 PATENT OFFICE FIRE CONTROL SYSTEM Hugh Murtagh, Brooklyn, N.

ummit, N. J., Gyroscope Company, Inc.,

Wittkuhns, S

Y., and Bruno A. assignors to Sperry Brwklyn, No Ya, a

corporation of New York Application January 10, 1934, Serial No. 706,034 11 Claims. .(01. 89-41) This invention relates to means for directing sights and/or guns toward targets, especially elevated targets, from a rolling ship, which automatically eliminates the trunnion tilt or cross leveling error that normally appears both in azimuth and elevation when the trunnions on which the sight or gun is mounted are inclined out of the horizontal plane. While many such devices have been proposed, the systems of the prior art cannot be adapted to anti-aircraft fire control, that is, for high elevation guns or sights as they all become inoperative when the gun or sight is elevated approximately 60 or more. Also, most of the systems of the prior art transmit the actual angular movements of the sight with respect to the ship and endeavor to introduce a separate trunnion tilt correction into said angles. Accordlngto our invention, however, we transmit from the sight the true azimuth and elevation 50 angles in which, of course, there is no trunnion tilt error, by stabilizing the sight in all planes.

One of the objects of our invention is to devise a trunnion tilt error eliminator which is equally efficient regardless of the angle of elevation of the gun or sight. Another object of the invention is to devise a system of this character in which the observer at the sight, in tracking a moving target, operates his elevating and training handwheels by exactly the same motions as he would use if he were fixed on land so that the movements of the handwheels provide an actual measure of the true altitude angle and true azimuth of the target whence therates of change of these quantities may be derived as data by a computer or predictor of the same type as may be employed on land. Other objects of the invention will be apparent from the following description.

Referring to the drawings illustrating several forms the invention may assume:

Fig. 1 is a plan view of a simple form of trunnion tilt correction device.

Fig. 2 is a side elevation of section.

Fig. 3 is a diagram illustrating how the invention is employed in'cooperation with the remote sight, gyro vertical, gyro compass, computer and the gun turret, the diagram showing two separate systems for two batteries.

Fig. 4 is a diagrammatic perspective view of a modified form of the computer.

Fig. 5 is a detail in elevation of the central portion of Figs. 1 and 2.

Fig. 6 is a detached sectional detail of a portion of Fig. 4.

the same, partly in In any system of naval anti-aircraft fire control, the position of the target has to be considered with'reference to two entirely separate sets of coordinates (1) a set of coordinates fixed in space comprising the angle of elevation of the target above the horizon which we may call the altitude angle" and the bearing of the target with respect to any compass bearing, such as a north-south line, which we may term the azimuth angle or azimuth of the target". Both the altitude and azimuth angles must be continuously known to enable the rates of apparent motion of the target to be known and its future position to be calculated with reference to the observing ship. Since, however, the gun and sight are on a moving ship, another set of coordinates are present with reference to the rolling deck and the fore and aft line of the ship. The elevation angle of the target with respect to the deck of the ship may be termed angular elevation and the bearing of the target, relative to the fore and aft line of the ship, may be termed train. Although the target may stand still, the elevation and train angles will obviously change with every change in the position of the ship. Also roll or pitch of the ship will alter the elevation angles and in most cases the train angle as well. But in the case assumed, there will be no change in the altitude and azimuth angles.

According to our invention, only the true altitude and azimuth angles are transmitted from the sight, from which the predicted position of the target may be calculated by any known form of standard computer or director, such as used on land. Finally, the predicted angular target positions are reconverted into future quadrant I elevation and future train angles from the known roll, pitch and yaw angles, and are transmitted to the gun.

In order to eliminate from the elevation and train agles, which would otherwise be transmitted from the sight, all effects of roll, pitch and yaw, or, in other words, to convert them into true altitude and azimuth angles, a reference plane stabilized with reference to the north-south line as well as horizontally, is employed, on which is positioned from the sight a device, the trunnion axis and angular elevation of which is maintained in fixed relation to the sight.

The base I in Fig. 1 may be considered to represent the horizontal surface of the sea and as the datum from which the altitude angle is measured. On brackets 2 and 2' on said base is an outer gimbal ring 3 pivoted on athwartships axis 4-4 and an inner ring 5 pivoted about a fore and aft axis 5 within the ring 3. Obviously if means were provided to cause the ring 5 to roll and pitch through the same angles that the ship rolls and pitches, the ring 5 may be considered to represent the deck of the ship. Such a motion may conveniently be imparted to the ring 5 by means of a pairof repeater motors PR and RR which are actuated respectively from transmitters PT and RT on the proper axes of a master gyro vertical or artifical horizon H of any approved design, such as shown in the copending'application of Bruno A. Wittuhns and' William Ans cott, Serial No. 562,282 filed September 11, 1931. The pitch motor PR turns the ring '3 directly through the pinion I geared to a gear 8 on one of trunnions 4 so as to rock the outer gimbal about a transverse axis. The motor RR is shown as operating through a differential 9, the planetary arm of which drives a gear III on a shaft H which passes loosely through the hollow shaft of the gear 8'and on the inner end of which is, a pinion l2 which drives the vertical gear sector l3 to rock the ring about the fore and aft axis 6. a The third arm of the diiferential carries a gear l4 meshing with gear 8, the object of the difierential being merely to prevent the pitching action from effecting the rolling mechanism.

Slidably mounted within ring 5 is a second ring l5 which is shown as provided with annular teeth l6 so that it may be turned from a followup motor F and may also turn an azimuth angle transmitter TT. Pivotally mounted inside of said ring is a half loop I! pivoted on trunnions, 18,18. These trunnions represent the trunnions azimuth by means of a gear 23 mounted on the lower end thereof so that it, may be turned to rotate the U-shaped bracket 2| from repeater motors TR and CR, hereinafter described.

At the same time the angle of elevation of the arm I9 may be controlled from an elevation repeater motor ER which is shown as geared to a shaft carrying at its inner end a pinion 25 which meshes with circular teeth 25 on a sleeve loosely mounted on the shaft 22. Sam sleeve carries at its upper end a bracket 21 (Fig. 5) having mounted thereon a vertical rack member 28, the teeth of which mesh with a gear 29 secured to the hub 30 of the arm l9.- Repeater ER may likewise be positioned from an altitude angle transmitter ET at the telescope 40. Hence the arm l9 may be positioned so that its train and altitudeangles, relative to the base I, agree with those observed by the target bearing telescope 40.

Elevating the arm will also elevate the half loop; I! which will consequently drive the elevation transmitter E'T through :an angle corrected for trunnion tilt error inv elevation. On said arm insulation 32 at the center thereof and the trolleys 3| and segments are placed "in circuit with "the above described follow-up motor F which turns the ring l5 through the annular rack teeth l6 and consequently turns the "train transmitter T'T. Therefore, any movement in train of the arm l9 will energize the motor F to cause t e ring l5 to follow the trolley and drive transmitter T'T through an angle corrected for trunnion tilt error in azimuth.

In our complete system we prefer to use two trunnion tilt correction or angle converting devices, one for maintaining the sight telescope on the target and for incidentally computing the true azimuth and elevation angles, and the second for maintaining the gun trained on the future position of thetargets.

Referring to Fig. 3, the target bearing telescope 40 is shown as rotated in azimuth by means of a pinion 4| and annular rack teeth 42 and is correspondingly operated in elevation about trun- .nion axis 45 by gear 46 operated from pinion 41. We prefer, however, that the observer have no direct means for elevating or training the telescope but that instead the usual training handwheel 48 be employed to operate train transmitter TT and the usual elevation controlling handle 49 be employed to operate elevation transmitter ET. The former is shown as operating the train repeater motor TR, which is geared to the gear 23 to position the shaft 22 and hence the trunnions of the arm IS in azimuth or in the plane of the surface of the sea. Since this is a true azimuth angle, the ship's heading may be introduced from the master compass C through the compass transmitter CT operating the compass repeater motor CR -which is connected through a differential 50 to the gear 23. Similarly the transmitter ET is connected to the repeater ER which positions the arm I9 in elevation, that is, through the altitude angle. The telescope, however, is turned about its two axes by means of separate repeater motors'T'R and ER, the first of which is actuated from the transmitter T'T operated from movements of the ring l5 in the plane of the ship's deck, and the second from the transmitter E'T operated from the elevational movements of the loop I1. Therefore, the telescope is maintained on the target regardless of the rolling, pitching or yawing of the ship so that the operator will not need to move the handwheels 48 and due to such causes. This is another way of saying that the motions imparted by the observer to such handwheels are the true altitude angles and azimuth angles of the target and, therefore, these transmitters may also feed into the computer or predicting mechanism within the box 52.

The computer or predictor, which is well known in the art and may be of the form described in .the copending application of E. W. Chafee, H. Murtagh and S. G. Myers, Serial No. 654,090 filed January 28, 1933, computes a required gun azimuth and angular altitude future elevation) for the gun to hit the "target, that is, the future angles in azimuth and altitude. These values, however, have to be reconverted into training angle (from the. ship's fore and aft line.) and quadrant elevation from the shipfs deck. operation is practically the converse of the operation above described. Hence we employ a second identical correction device operating between the computer 52 and the gun turret G. For this purpose the future elevation, as given by the computer, is shown as operating the elevation repeater motor ER to give the required elevation to the arm IS. The gun azimuth is transmitted to the repeater motor TR" where it is combined with the course received from the compass by the compass repeater motor CR' through the difierential 50' andpitch and roll are again fed into the repeater motors RR'andPR from the same may assume.

gyro vertical. Therefore. the transmitter T'T will transmit the proper training angle to the gun and is shown as actuating the repeater motor TR' which actuates the gun in train either directly or through a follow-the-pointer indicator I at the gun. Similarly, the quadrant elevation with respect to the ship is transmitted from transmitter E'T to the repeater motor E'R' at the gun which may also actuate a follow-thepointer indicator I or suitable power driven follow-up mechanism. If another battery is employed, an additional computer If and set of trunnion tilt correctors, shown as within a box 55, are employed. The same gyro vertical and gyro compass may be used as before. a

Fig. 4 illustrates another form our invention In this figure the several rings,

' transmitters and repeater motors are correspondingly markedso as to be easily recognized, the outer ring being shown at 3' and the inner ring at 5'. In this. case, however, the pitch and roll repeater motors PR and RR are positioned adjacent their respective axes L- i and 6-6, the

of the ring l5, we employ a half loop 88 mounted for turning about a vertical axis in a fixed bracket 6| above the rings. The inner surface of said loop is provided with a trackway in which slides a ring sector 82 provided with annular rack teeth 63. The angular position of said sector 62 in elevation may be adjusted by turning the inner shaft 64 which turns a pinion 65 meshing with the teeth 63. The entire loop 60, however, may

be turned in-azimuth within the bracket 6| by means of the bevel gear 66, the hollow hub of which carries the loop 68. The position of, the

loop- 60 and, its driving gear 86 corresponds in' general to the position of the U-shaped bracket 2| and the driving gear 23 in Figs. 1 and 2 so that said loop may be turned in azimuth differentially from train repeater motor TR and compass re-' peater motor CR through differential and gearing 16. The position of the sector 62 in elevation corresponds somewhat to the position of the arm I9 in elevation and hence said sector may be driven from repeater motor ER which drives bevel gearing 11 through gearing I8 and unwinding differential I9, gear 11 driving second bevel gear 88 on shaft 64 above described. The differential I9 is for the purpose of preventing elevational adjustments from efiecting azimuth adjustments and vice versa and isplaced between gears 18' and 16.

On bracket I16 is journalled a large gear 82 on which is mounted a pair of journal arms 83 which pivotally support a cross shaft 84. A gear sector 85 is shown as fixed to one .bracket 83. Meshing with said sector is a pinion 88 on elevation transmitter ET which is 'secured to a frame work 8.! so that rocking of said framework on shaft 84 will actuate the transmitter. Said framework in turn carries a second follow-up contact maker or transmitter 88 and also plvotaily supports on trunnions 88 at right angles to shaft 84 a U-shaped bracket 88 which carries a pin 9| fixed to the aforesaid ring 82. With the parts positioned as shown in the drawings, that is. with the rings 3', 5 horizontal and the shaft 84 parallel to or in line with axis 8, 6 and with the plane of loop 68 lying in the axis 44, it is obvious that movement of the loop 62 in elevation will rock bracket 90 and framework 81 about the axis of shaft 84 without moving the bracket 80 on its trunnions 89. In case the plane of loop 88 is intercardinal and rolling and pitching occur,

W The above described mechanism will give sufiie.

ciently accurate results for most practical purposes. However, fora theoretically accurate solution, the stabilized ring 5' should be taken as the true horizontal reference plane, while the ship itself should be considered the rolling ship instead of assuming the opposite as was done in Fig. 4. .To accomplish this purpose the only changes necessary would be to transfer the compassrepeater motor CR and the train repeater TR together with the connecting differential to actuate the large gear 82 in place of the followup motor F. The follow-up motor F would then replace the two motors CR and TR to actuate the gear 18, the motor F being actuated as before from the transmitter 88. The train angle would then be taken off from'a transmitter T'T also connected to gear I6. In elevation, the elevation or altitude angle repeater motor ER would be interchanged in position with the elevation transmitter E'T so that the elevation angle would be fed into and position the frame 80 and the sight or quadrant elevation angle would be transmitted from a transmitter E'T connected to gear 18. a From the foregoing the operation of our invention will be readily apparent. The importance or advantage of employing a follow-up system to actuate the azimuth correction may be appreciated if it is realized that the trunnion tilt corre'ction varies from zero to infinity, because it varies as a function of the tangent of the angle of elevation ofthe gun or sight. If attempt is made to actuate the azimuth correction by mechanical linkages. the output will become several times the input of the linkage as the angle passes 60, so that such a linkage becomes inoperative before the 90 elevation is reached.

Another advantage of this system is that it enables the device to be slowed down in action so as not to run away from the guns. The speed of rotating a heavy mount is, of course, limited and at high angle elevations and where the ship is rolling with a period of a few seconds it would be impossible for the gun to keep up with an ordinary correction device. With our invention, however, the speed at wh ch the follow-up motor F on corrector II actuates the ring IE or gear 82 may be madeso as not to exceed the usual rate of turn of the guns. Ths of course will result in the trolle'. 3! running over at a substantial angle on the hop il. By putting in extra insulating sections 8 and 9! on each side of the central section 32, we may connect to the ou ermost live sections to a signal lamp 9! which may be placed at the gun and which, when lighted, will signal not to fire. The gunner then will only fire when the lamp is out and when the follow-up pointers are matched.

In accordance with the provisions of the patent statutes, we have herein described the principle and operation of our invention, together with the apparatus which we now consider to represent the best embodiment thereof, but we desire to have it understood'that the apparatus shown is only illustrative and that the invention can be carried out by other means. Also, while it is designed to use the various features and elements in the combination and relations described, some of these maybe altered and others omitted without interfering with the more general results outlined, and the invention extends to suclruse.

Having described ourinvention, what we claim and desire to secure by Letters Patent is:

1. In a naval anti-aircraft fire control system, the combination with a sight mounted for rotation in the plane of the ships deck and for elevation in a plane perpendicular thereto, a master compass and a master vertical, of a train transmitter and an elevation transmitter at said sight but disconnected therefrom, means for eliminating the effect of the ships roll and yaw including a part stabilized from said vertical, and parts positioned in azimuth and elevation from said transmitters and said compass, connections between said parts reproducing the displacement of the telescope in azimuth and elevation due to roll, pitch and yaw and the original set in angles, and transmitters actuated thereby for rotating and elevating said telescope.

2. In a naval anti-aircraft fire control system, the combination with a sight mounted for rotation in the plane of the ships deck and for elevation in a plane perpendicular thereto, a master compass and a master vertical, of a train transmitter and an elevation transmitter at said sight but disconnected therefrom, a trunnion tilt error preventing device including a part stabilized from said vertical, and parts positioned in azimuth and elevation from said transmitters and said compass, connections between said parts reproducing the displacement of the telescope in azimuth and elevation due to roll, pitch and yaw and the original set in angles, transmitters actuated thereby for rotating and elevating said telescope, and a computer also actuated from said first mentioned transmitters.

3. In a naval fire control system, the combination with a sight mounted for rotation in the plane of the ships deck and for elevation in a plane perpendicular thereto, a master compass and a master vertical, of a train transmitter and an elevation transmitter at said sight but discon nected therefrom, a trunnion tilt error preventing device including a part stabilized from said verticaband parts positioned in azimuth and elevation from said transmitters and said compass, connections between said parts reproducing the displacement of the telescope in azimuth and elevation due to roll, pitch and yaw and the original set in angles, transmitters actuated thereby for rotating and elevating said telescope, a computer also actuated from said first mentioned transmitters, a second similar device having similar parts stabilized from said vertical and compass and actuated from said computer, and transmitters actuated thereby for positioning the gun to hit the target.

4. In a naval anti-aircraft fire control system, the combination witha sight mounted for rotation in the plane of the ships deck and for elevation in a plane pe pendicular thereto and means for maintaining horizontal and directional reference planes, of a train transmitter and an elevation transmitter at said sight but disconnected therefrom, means for eleminating the effect of the ships roll, pitch and yaw including parts positioned diiferentialiy from said transmitters and said first named means, connections between said parts reproducing the displacement of the telescope in azimuth and elevation due to roll, pitch and yaw and the original set in angles, and transmitters actuated thereby for rotating and elevating said telescope.

5. In a naval fire control system, the combination with a sight mounted for rotation in the plane of the ships deck and for elevation in a plane perpendicular thereto and means for maintaining horizontal and directional reference planes, of a train transmitter and an elevation transmitter at said sight but disconnected therefrom, a. trunnion tilt error preventing device including parts positioned differentially from said transmitters and said means, connections between said parts reproducing the displacement of the telescope in azimuth and elevation due to roll, pitch and yaw and the original set in angles, transmitters actuated thereby for rotating and elevating said telescope, a computer also actuated from said first mentioned transmitters, a second trunnion tilt error preventing device having similar parts stabilized from said first named means and actuated from said computer, and transmitters actuated thereby for positioning the gun to hit the target.

6. In a trunnion tilt error preventing device for naval anti-aircraft guns, a gimbal ring, meansfor causing the same to roll and pitch on the ship as the ship rolls and pitches, a part rotatably mounted in the plane thereof, a second part pivotally mounted on a trunnion axis secured on said first part, a third part rotatably mounted in a plane representing the horizontal, a fourth part trunnioned thereon to tilt in a perpendicular plane representing vertical, a connection between said second and fourth parts to cause them to move together in elevation, means for turning and elevating said fourth part from the sight, and a follow-up drive brought into action by relative lateral displacement of said second and fourth parts for turning said first part in said ring.

7. In a trunnion tilt error preventing device for naval anti-aircraft guns, a gimbal ring, means for causing the same to roll and pitch with respect to the ship; a part rotatably mounted in the plane thereof, a second part pivotally mounted on a trunnion axis on said first part, a third part rotatably mounted in a planerepresenting the horizontal, a fourth part trunnioned thereon to tilt in a vertical plane, means for turning and elevating said fourth part from the sight, a follow-up drive brought into action by relative lateral displacement of said second and fourth parts for turning said first part in said ring, and a transmitter actuated thereby for turning the sight.

8. In a trunnion tilt error preventing device for naval anti-aircraft guns, a gimbal ring, means for stabilizing the same against the roll and pitch of the ship, a part rotatably mounted in the plane thereof, a second part pivotally mounted on a trunnion axis secured thereto, a third part rotatably mounted in a plane fixed on the ship, a fourth part trunnioned thereon to tilt in a perpendicular plane, a connection between said second and fourth parts to cause them to move together in elevation, means for turning and elevating said fourth part from the sight and compass, and a follow-up drive brought into action by relative lateral displacement of said second and fourth parts for turning said first part in said ring.

9. In a trunnion tilt error preventing device for ships, a universally mounted member, means for stabilizing the same from a remote horizontal reference plane, means for fixing the same in azimuth from a master compass, a second member on an unstabilized part, means for elevating one of said members through the sight angle, means for elevating the other member from the first, and follow-up power driven means for rotating the other member in its plane responsive to relative azimuth movements of the first member.

10. In a trunnion tilt error preventing device for ships, a universally mounted member, means for stabilizing the same from a remote horizontal reference plane, means for fixing the same in azimuth from a master compass, a second member on an unstabilized part,'means for elevating one of said members through the sight angle, means for elevating the other member from the first, slow acting follow-up power-driven means for rotating the other member in its plane responsive to relative azimuth movements of the first member, and signaling means for preventing firing when said two members are not substantially in agreement.

11. In a naval fire control system, a sight, means for converting the elevation and train angles thereof with reference to the plane of the ships deck and fore and aft line into true present altitude and azimuth angles, a computing device for computing therefrom the future altitude and azimuth angles, a second converting means for reconverting said last-named angles into quadrant elevation and future train angles for the gun, and means for preventing said second device from operating faster than the normal speed of train of the gun.

12. In a trunnion tilt error preventing device for naval anti-aircraft guns, a gimbal ring, means for causing the-same to roll and pitch with respect to the ship, a part rotatably mounted in the plane thereof, asecond part pivotally mounted on a trunnion axis on said part, a third part rotatably mounted in a plane representing the horizontal, a fourth part trunnioned thereon to tilt'in a vertical plane, means for turning and elevating said fourth part from a future position computing device, a follow-up drive brought into action by relative lateral displacement of said second andfourth parts for turning said first part in said ring, and atransmitter actuated thereby for causing turning of the gun,

13. In a naval'fire control system, the combination with a predicting computer of the type also adapted for land use and adapted 'to continuously generate future azimuth and altitude angles from present azimuth and altitude angles, a sight mounted for movement about axes parallel and perpendicular to the ships deck, means stabilized against the ships roll, pitch and yaw and having a part positioned in accordance with the position of said sight about like axes, means actuated thereby for eliminating the ships roll, pitch and. yaw movements from the sight, and means for feeding the true azimuth and altitude angular movements of said line of sight of the sight into said computer.

14. A naval fire control system as claimed in claim 13, having a second stabilized means, a part pivoted on a non-stabilized trunnion axis and positioned in azimuth and elevation from the future angles generated by said computer, and means actuated thereby for transmitting future train and angular elevation to the gun, whereby the line of fire of the gun is stabilized on the target in azimuth and in elevation.

.15. In a trunnion tilt error preventing device for naval anti-aircraft guns, a gimbal ring, means for causing the same to roll and pitch on the ship as it rolls and pitches, a part rotatably mounted in the plane thereof, a second part pivotally mounted on a trunnion axis on said first part, a third part rotatably mounted in a plane representing the horizontal, a fourth part trunnioned thereon to tilt in a perpendicular plane representing the vertical, a connection between said second and fourth parts to cause them to move together in elevation, means for turning one of said first or third parts from the sight, means for elevating one of said second or fourth parts from the sight, and a follow-up drive brought into action by relative lateral displacement of said second and fourth parts for turning the other of said first or third parts.

16. In a. naval fire control system, a sight, means for converting the elevation and train angles thereof with reference to the plane of the 'ships deck and fore and aft line into true present altitude and azimuth angles, including means actuated from said first named means for moving said sight, a computing device for computing future altitude and azimuth angles, means for continuously feeding said present altitude and azimuth angles of said sight into said computer, and a second converting means actuated from the output of said device for reconverting said last-named angles into quadrant elevation and future train angles for the gun with reference to the ships deck and fore and aft line.

, 17. In a naval fire control system, the combination with a trunnion mounted sight and gun, of a pair of devices for converting true azimuth and altitude angles into train and elevation angles with respect to the ships heading and the ships deck, means for actuating one of said devices indirectly from transmitters at the sight, means at said device for keeping the sight on the target by turning said transmitters, and a predictor for feeding future true azimuth and altitude angles into the second of said devices, said gun being controlled in elevation and train from the output of said second device.

HUGH MIIRTAGH. BRUNO A. WI'I'I'KUHNS.

CERTIFICATE OF CORRECTI ON.

ant No 2,069,417. d February 2, 1937.

HUGH MURTAGH, ET AL.

It is hereby certified that error appears in the above numbered patent uiring correction as follows: In the signature to the drawings, sheets 2 and 3, strike out the name and word "Arthur L. Rawlings and"; and

at the said Letters Patent should be read with this correction therein it the same may conform to the 'record of the case in the Patent Office, Signed and sealed this 23rd day of February, A. D. 1937.

Henry Van Arsdale L1) Acting Commissioner of Patents. 

